Pregnancy risks rise with heat and smoke exposure

Pregnancy is a delicate time, and fresh evidence shows that wildfire smoke and extreme heat may add extra risk – especially for families in climate-stressed neighborhoods.

The study suggests that exposure even a month before conception can shape a baby’s weight at birth.

Researchers at the University of Southern California tracked more than 700 pregnancies across Los Angeles between 2016 and 2020.

Study lead author Roxana Khalili is a researcher in the Department of Population and Public Health Sciences at the Keck School of Medicine of USC.

“We already know that poor air quality is associated with adverse health outcomes, and that pregnant women and fetuses are especially vulnerable,” said Khalili.

Location impacts pregnancy outcomes

“Where you live makes a difference in your health,” said Khalili. “So does the timing of your exposure during or immediately before pregnancy.”

“We wanted to better understand how these risks might differ for women who lived in neighborhoods that experience more climate related stressors and have fewer resources to deal with them.”

Using detailed smoke maps from CalFIRE and NOAA, the team estimated how much fine particle pollution reached each participant’s home on every day.

The researchers paired the fire pollution data with weather data to capture heat, humidity, and wind. Together, those numbers revealed when each mother faced high smoke or heat stress.

Pregnancy risks rise with wildfire days

“Overall, we found consistent associations between increased exposure to wildfire smoke and heat stress during preconception and the first trimester with the odds of having an SGA infant,” Khalili said.

Babies classified as small-for-gestational-age (SGA) weigh below the 10th percentile for their age.

The team linked moderate smoke exposure in early pregnancy to low birth weight under five pounds, eight ounces.

Living in the hottest, most climate-vulnerable parts of the city raised the stakes. For women in these areas, the effect of heat stress before conception on the chance of an SGA birth nearly doubled.

Fenton Z-scores, a marker of how an infant’s size differs from the average, also fell as wildfire days piled up during pregnancy.

More than just staying indoors

“Understanding what’s happening to women during wildfires and excessively hot days could help us identify protective measures, develop guidance, and plan interventions,” said Khalili.

Staying indoors, running air filters, and using air conditioning can help. However, the researchers stress that broader community solutions are needed.

“As the recent Los Angeles fires have demonstrated, infrastructure, socioeconomic, and health vulnerabilities can combine with excessive climate and environmental factors to magnify health risks,” said Rima Habre, director of USC’s CLIMA Center.

“It is only by looking at the cumulative impacts of burdens communities are facing, now and into the future, that we can start to truly quantify health risks of climate hazards and target interventions to strengthen community resilience.”

Pregnant stress linked to surroundings

Pregnancy is shaped by more than genetics or individual behavior. The surrounding environment – both physical and social – plays a powerful role in maternal and infant health.

Factors like air quality, temperature, housing conditions, and access to health care can all affect outcomes.

For families in under-resourced communities, these stressors often overlap, compounding the risks during pregnancy.

Public health experts are increasingly calling for a more holistic approach to prenatal care. This means looking beyond clinical checkups to also consider neighborhood-level interventions.

Better planning protects expectant mothers

Expanding access to clean air, cool spaces, nutritious food, and mental health support can help ease the burden on expectant mothers.

Another crucial step is preparing communities for climate-related challenges with better urban planning and emergency response systems.

Pregnancy is a vulnerable time, but it’s also an opportunity to make meaningful change. By protecting the health of pregnant people today, we’re investing in the well-being of future generations.

As climate-related hazards grow more frequent, ensuring healthier pregnancies will require more than individual action.

Protection for expecting mothers will demand community-wide support, informed policies, and sustained attention to the environments in which people live, work, and grow families.

The full study was published in the journal Environmental Science & Technology.

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